Electronic component and semiconductor device, method of making the same and method of mounting the same, circuit board, and electronic instrument

ABSTRACT

A semiconductor device with its package size close to its chip size has a stress absorbing layer, allows a patterned flexible substrate to be omitted, and allows a plurality of components to be fabricated simultaneously. There is: a step of forming electrodes ( 12 ) on a wafer ( 10 ); a step of providing a resin later ( 14 ) as a stress relieving layer on the wafer ( 10 ), avoiding the electrodes ( 12 ); a step of forming a chromium layer ( 16 ) as wiring from electrodes ( 12 ) over the resin layer ( 14 ); and step of forming solder balls as external electrodes on the chromium layer ( 16 ) over the resin layer ( 14 ); and a step of cutting the wafer ( 10 ) into individual semiconductor chips; in the steps of forming the chromium layer ( 16 ) and solder balls, metal thin film fabrication technology is used during the wafer process.

This is a Divisional of application Ser. No. 12/216,145, filed Jun. 30,2008, which in turn is a Divisional of application Ser. No. 11/320,583,filed Dec. 30, 2005, now U.S. Pat. No. 7,470,979, which in turn is aContinuation of application Ser. No. 10/804,039, filed Mar. 19, 2004,now U.S. Pat. No. 7,049,686, which in turn is a Continuation ofapplication Ser. No. 10/254,600, filed Sep. 26, 2002, now U.S. Pat. No.6,730,589, which in turn is a Divisional of application Ser. No.09/117,510, filed Apr. 22, 1999, now U.S. Pat. No. 6,475,896, whichclaims the benefit of PCT/JP97/04437, filed Dec. 4, 1997. The entiredisclosure of the prior applications is hereby incorporated by referenceherein in its entirety.

BACKGROUND

The invention relates to an electronic component and a semiconductordevice, a method of making the same and method of mounting the same, acircuit board, and an electronic instrument, and in particular relatesto a compact electronic component and a semiconductor device having apackage size close to the chip size, a method of making the same andmethod of mounting the same, a circuit board, and an electronicinstrument.

To pursue high-density mounting in semiconductor devices, bare chipmounting is the ideal. However, for bare chips, quality control andhandling are difficult. In answer to this, CSP (chip scale package), orpackages whose size is close to that of the chip, have been developed.

Of the forms of CSP semiconductor device developed, one form has aflexible substrate provided, patterned on the active surface of thesemiconductor chip, and on this flexible substrate are formed aplurality of external electrodes. It is also known to inject a resinbetween the active surface of the semiconductor chip and the flexiblesubstrate, in order to absorb the thermal stress. In Japanese PatentApplication Laid-Open No. 7-297236, as the flexible substrate isdescribed the use of a thin film carrier tape.

In these methods of fabricating a semiconductor device, a semiconductorchip is cut from a wafer, and individual semiconductor chips are mountedon a flexible substrate. As a result, not only is the patterned flexiblesubstrate necessary, but also a process is required to mount eachindividual semiconductor chip on the flexible substrate, and thereforethe devices used in each of the steps of the process must bespecial-purpose equipments, and the cost is increased.

Besides, a semiconductor device to which a CSP type package is appliedis surface-mounted, and has a plurality of bumps for mounting on acircuit board. The surface on which these bumps are formed is preferablyprotected by the provision, for example, of a photosensitive resin.

However, since a photosensitive resin is electrically insulating, andmounting while it remains on the bumps is not possible, it is necessaryto remove the photosensitive resin from the top of the bumps. Here, inorder to remove a part of the photosensitive resin, lithography must beapplied, and this results in the problem of an increased number ofsteps.

In this way, a conventional semiconductor device suffers from inferiorefficiency in the process from fabrication to mounting.

The invention has as its object the solution of the above describedproblems, and this object subsists in the provision of an electroniccomponent and a semiconductor device, a method of making the same andmethod of mounting the same, a circuit board, and an electronicinstrument such that the process from fabrication to mounting can becarried out efficiently.

SUMMARY

The method of making a semiconductor device of the invention comprises:

a step of providing a wafer on which are formed electrodes;

a step of providing a stress relieving layer on the wafer in such a wayas to avoid at least a part of the electrodes;

a step of forming wiring over the stress relieving layer from theelectrodes;

a step of forming external electrodes connected to the wiring above thestress relieving layer; and

a step of cutting the wafer into individual pieces.

According to the invention, the stress relieving layer is formed on thewafer, and further thereon the wiring and external electrodes arelaminated, so that the fabrication process proceeds as far as formingthe semiconductor package while still in the wafer stage; this obviatesthe need for a substrate such as a patterned film with preformedexternal electrodes.

Here, the stress relieving layer refers to a layer which relieves thestress caused by distortion between the motherboard (mounting board) andsemiconductor chip. For example, such stresses may be generated when thesemiconductor device is mounted on the mounting board and whensubsequently heat is applied. As the stress relieving layer is selecteda material which is flexible or a gel material.

Besides, since the wiring between the electrodes and the externalelectrodes can be formed freely according to the requirements of thedesign, the layout of the external electrodes can be determinedregardless of the layout of the electrodes. As a result, withoutchanging the circuit design of the elements formed on the wafer, varioussemiconductor devices with the external electrodes in differentpositions can easily be fabricated.

Furthermore, according to the invention, after the stress relievinglayer, wiring and external electrodes are formed on the wafer, the waferis cut, to obtain individual semiconductor devices. As a result, theformation of the stress relieving layer, wiring and external electrodeson a large number of semiconductor devices can be carried outsimultaneously, which is preferable when quantity production isconsidered.

As the stress relieving layer is used, for example, a resin with aYoung's modulus of not more than 1×10¹⁰ Pa.

In the step of providing the stress relieving layer, a photosensitiveresin may be applied to the wafer in such as way as to include theelectrodes, and the photosensitive resin may be removed from the regioncorresponding to the electrodes, whereby the stress relieving layer maybe provided.

The stress relieving layer may be provided by printing the resinconstituting the stress relieving layer.

The photosensitive resin may be selected from the set consisting ofpolyimide resin, silicone resin, and epoxy resin.

The stress relieving layer may have a plate with holes formedcorresponding to the electrodes adhered to the wafer; and the plate mayhave a coefficient of thermal expansion intermediate between those ofthe semiconductor chip and a circuit board on which the semiconductorchip is mounted.

By this means, since the coefficient of thermal expansion of the plateis intermediate between the coefficient of thermal expansion of thesemiconductor chip and the coefficient of thermal expansion of theboard, stress generated by differences in the coefficient of thermalexpansion values can be absorbed. Besides, since the plate used heresimply has holes formed therein, its formation is simpler than that of apatterned substrate.

The stress relieving layer may be formed of a resin in a plate form, andthe plate form of resin may be adhered to the wafer.

By this means, in contradistinction to a patterned substrate, therequired form can be formed easily.

The wafer used in the step of providing the wafer may have formed aninsulating film, except in the regions of the electrodes and the regioncut in the step of cutting.

Before the step of forming wiring, there may further be a step ofroughening the surface of the stress relieving layer.

After the step of forming external electrodes and before the step ofcutting, there may further be a step of applying a photosensitive resinto form a film on the surface of formation of the external electrodes toinclude the external electrodes, and a step of carrying out isotropicetching with respect to the photosensitive resin until the externalelectrodes are exposed.

After the step of forming external electrodes and before the step ofcutting, there may further be a step of applying an organic film to forma film on the surface of formation of the external electrodes to includethe external electrodes.

As the organic film may be used a flux such that when heated the residueis changed by a chemical reaction into a thermoplastic polymer resin.

The wiring may be bent over the stress relieving layer.

At the junction of the wiring and the electrodes, the width of thewiring may be greater than the width of the electrodes.

In the invention, the stress relieving layer may be formed, and over thestress relieving layer the wiring may be formed, and thereafter a solderportion may be formed by electroless plating, and the solder portion maybe formed into the external electrodes.

In the invention there may further be:

a step in which the stress relieving layer is formed and a conductinglayer is formed on the stress relieving layer; a step in which a solderportion is formed over the conducting layer by electroplating; a step offorming the conducting layer into the wiring; and a step of forming thesolder portion into the external electrodes.

In the invention there may further be:

a step in which a protective film is formed over the wiring in a regionavoiding the external electrodes.

The solder portion may be formed on a previously formed seat on thewiring.

The solder portion may be formed on a solder film formed by a platingprocess.

In the invention there may further be:

a step in which after the step of forming the wiring a protective filmis formed on the wiring; a step in which before the step of formingexternal electrodes in at least a part of the region of the protectivefilm corresponding to the external electrodes openings are formed; andin the step of forming external electrodes, a solder cream may beprinted in the openings and a wet-back process may be carried out,whereby the external electrodes are formed.

In the invention there may further be:

a step in which after the step of forming wiring, a protective film isformed on the wiring; and a step in which before the step of formingexternal electrodes in at least a part of the region of the protectivefilm corresponding to the external electrodes openings are formed; andin the step of forming external electrodes, a flux may be applied withinthe openings, and thereafter on each opening a piece of solder may bemounted, whereby the external electrodes are formed.

The protective film may be formed of a photosensitive resin, and theopenings may be formed by a process including exposure and developmentsteps.

In the invention, before the wafer is cut into individual pieces, theremay be a step in which a protective member is provided on the surface ofthe wafer opposite to the surface on which the electrodes are provided.

By this means, since the rear surface of the semiconductor device iscovered by a protective film, the occurrence of damage can be prevented.

The method of making a semiconductor device of the invention comprises:

a step in which a plurality of bumps are formed on one surface of awafer;

a step in which resin is applied to the surface until the bumps areincluded;

a step in which isotropic dry etching is applied to the face of theresin; and

a step in which the wafer is cut into individual pieces; and wherein thedry etching step ends after the bumps are exposed and before the surfaceis exposed.

According to the invention, a resin is applied to one surface of awafer. This resin is applied over the bumps, but since the bumps projectfrom the surface, the resin is applied more thinly over the bumps thanin other regions.

Then when isotropic dry etching is applied to the resin face, since theresin is removed from all regions equally, the bumps where the resin isthinnest are exposed first. At this point the wafer surface is not yetexposed, and the dry etching is stopped at this point. In this way, awafer can be obtained in which the bumps are exposed, but the regionsother than the bumps are protected by a resin covering.

Thereafter, the wafer can be cut into individual pieces to obtain thesemiconductor devices.

The method of making an electronic component of the invention comprises:

a step in which a plurality of electronic elements are integrally formedin substrate form;

a step in which a stress relieving layer is provided at least in theregion where external electrodes are formed on the substrate formelectronic elements;

a step in which the external electrodes are formed on the stressrelieving layer; and

a step in which the substrate form electronic elements are cut intoindividual items.

According to the invention, since there is a stress absorbing layer,stresses caused by differential thermal expansion between the electroniccomponent and the board on which it is mounted can be absorbed. Aselectronic components, for example, may be cited resistors, capacitors,coils, oscillators, filters, temperature sensors, thermistors,varistors, variable resistors, fuses, and semiconductor devices.

The method of making an electronic component of the invention comprises:

a step in which a plurality of bumps are formed on a circuit boardmounting surface of an electronic element;

a step in which resin is applied to the mounting surface until the bumpsare included; and

a step in which isotropic dry etching is applied to the surface of theresin; and wherein the dry etching step ends after the bumps are exposedand before the mounting surface is exposed.

According to the invention, a resin is applied to the mounting surfaceof an electronic element. This resin is applied over the bumps, butsince the bumps project from the mounting surface, the resin is appliedmore thinly over the bumps than in other regions.

Then when isotropic dry etching is applied to the resin surface, sincethe resin is removed from all regions equally, the bumps where the resinis thinnest are exposed first. At this point the mounting surface is notyet exposed, and the dry etching is stopped at this point. In this way,an electronic component can be obtained in which the mounting surface isprotected by a resin covering, but avoiding the bumps.

In the invention, as the electronic element may be used a semiconductorelement.

The method of making an electronic component of the invention comprises:

a step in which a plurality of bumps are formed on one surface of anelectronic element board;

a step in which resin is applied to the surface until the bumps areincluded;

a step in which isotropic dry etching is applied to the face of theresin; and

a step in which the electronic element board is cut into individualitems; and wherein the dry etching step ends after the bumps are exposedand before the mounting surface is exposed.

According to the invention, a resin is applied to one surface of anelectronic element board. This resin is applied over the bumps, butsince the bumps project from the surface, the resin is applied morethinly over the bumps than in other regions.

Then when isotropic dry etching is applied to the resin surface, sincethe resin is removed from all regions equally, the bumps where the resinis thinnest are exposed first. At this point the surface of theelectronic element board is not yet exposed, and the dry etching isstopped at this point. In this way, an electronic element board can beobtained in which the bumps are exposed, but the regions other than thebumps are protected by a resin covering.

Thereafter, the electronic element board can be cut into individualpieces to obtain the semiconductor devices.

The electronic component of the invention has the external electrodesover the stress relieving layer. For example, as an electronic componentmay be cited a semiconductor device.

The electronic component of the invention is manufactured by the abovedescribed method, and has a plurality of bumps formed on a mountingsurface, and a resin covering the mounting surface avoiding at least theupper extremities of the bumps.

The semiconductor device of the invention comprises:

a semiconductor chip having electrodes;

a stress relieving layer provided on the semiconductor chip so as toavoid at least a part of the electrodes;

wiring formed from the electrodes over the stress relieving layer; and

external electrodes formed on the wiring over the stress relievinglayer.

The wiring may be formed of any selected from the group comprisingaluminum, aluminum alloy, chromium, a layer of copper or gold, twolayers of copper and gold, two layers of chromium and copper, two layersof chromium and gold, two layers of platinum and gold, and three layersof chromium, copper and gold.

The wiring may be formed of a chromium layer over the stress relievinglayer and a layer of at least one of copper and gold.

The wiring may include a titanium layer.

Titanium has excellent moisture resistance, and therefore lead breakagesdue to corrosion can be prevented. Titanium also has preferred adhesionwith respect to polyimide resin, and provides excellent reliability whenthe stress absorbing layer is formed of polyimide resin.

The wiring may have one of a layer of nickel formed over the titaniumlayer and two layers of platinum and gold.

In the semiconductor device, the semiconductor chip may have aprotective film on the surface opposite to the surface having theelectrodes.

The protective film may be of a material different from the materialused for the wafer, and may have a melting point not less than themelting point of solder.

In the semiconductor device, the semiconductor chip may have a radiatoron the surface opposite to the surface having the electrodes.

The semiconductor device is manufactured by the above described method,and has a plurality of bumps formed on a mounting surface, and a resincovering the mounting surface avoiding at least the upper extremities ofthe bumps.

The method of mounting an electronic component of the inventioncomprises:

a step of applying flux to a mounting surface having a plurality ofbumps formed on an electronic element until the bumps are included; anda reflow step of mounting the bumps on wiring oh a circuit board withthe flux interposed.

According to the invention, since a flux is applied to the mountingsurface, even after mounting is completed with the reflow process, theflux remains to cover and protect the mounting surface. Moreover, it isnot necessary to apply the flux so as to avoid the bumps, and theapplication can simply be made to the whole mounting surface includingthe bumps, so that the application can be carried out simply.

In the invention, as the electronic element may be used a semiconductorelement.

On the circuit board of the invention is mounted the above describedsemiconductor device.

On the circuit board of the invention is mounted the above describedsemiconductor device having a plurality of bumps formed on a mountingsurface, and a resin covering the mounting surface avoiding at least theupper extremities of the bumps.

The electronic instrument of the invention has this circuit board.

The electronic instrument of the invention has a circuit board on whichis mounted a semiconductor device having a plurality of bumps formed ona mounting surface, and a resin covering the mounting surface avoidingat least the upper extremities of the bumps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E illustrate a first embodiment of the method of making asemiconductor device;

FIGS. 2A to 2E illustrate the first embodiment of the method of making asemiconductor device;

FIGS. 3A to 3D illustrate the first embodiment of the method of making asemiconductor device;

FIGS. 4A to 4C illustrate the first embodiment of the method of making asemiconductor device;

FIG. 5 is a plan view showing the first embodiment of the semiconductordevice;

FIGS. 6A to 6C illustrate a second embodiment of the method of making asemiconductor device.

FIGS. 7A to 7C illustrate the second embodiment of the method of makinga semiconductor device;

FIGS. 8A to 8D illustrate a third embodiment of the method of making asemiconductor device;

FIGS. 9A to 9D illustrate the third embodiment of the method of making asemiconductor device;

FIG. 10 illustrates a fourth embodiment of the method of making asemiconductor device;

FIGS. 11A to 11C illustrate a fifth embodiment of the method of making asemiconductor device;

FIGS. 12A to 12C illustrate the fifth embodiment of the method of makinga semiconductor device;

FIGS. 13A to 13D illustrate a sixth embodiment of the method of making asemiconductor device;

FIGS. 14A to 14E illustrate a seventh embodiment of the method of makinga semiconductor device;

FIGS. 15A to 15E illustrate the seventh embodiment of the method ofmaking a semiconductor device;

FIGS. 16A to 16D illustrate the seventh embodiment of the method ofmaking a semiconductor device,

FIGS. 17A to 17C illustrate the seventh embodiment of the method ofmaking a semiconductor device;

FIG. 18 is a plan view showing the seventh embodiment of semiconductordevice;

FIGS. 19A and 19B illustrate an eighth embodiment, of the method ofmounting of a semiconductor device;

FIG. 20 shows an example in which the invention is applied to anelectronic component for surface mounting;

FIG. 21 shows an example in which the invention is applied to anelectronic component for surface mounting;

FIG. 22 shows an example in which a protective layer is formed on asemiconductor device to which the invention is applied;

FIG. 23 shows an example in which a radiator is provided on thesemiconductor device to which the invention is applied;

FIG. 24 shows a circuit board on which is mounted an electroniccomponent fabricated by application of the method of the invention; and

FIG. 25 shows an electronic instrument provided with a circuit board onwhich is mounted an electronic component fabricated by application ofthe method of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The preferred embodiments of the invention are now described withreference to the drawings.

First Embodiment

FIG. 5 is a plan view of a semiconductor device of this embodiment. Thissemiconductor device is classified as a so-called CSP, and has leads 3formed extending toward the center of an active surface la fromelectrodes 12 formed around the periphery of a semiconductor chip 1, andon each lead 3 is provided an external electrode 5. All of the externalelectrodes 5 are provided on a stress relieving layer 7, so that whenmounted on a circuit board (not shown in the drawings) the stresses canbe relieved. Besides, in the region other than that of the externalelectrodes 5, a solder resist layer 8 is formed as a protective film.

The stress relieving layer 7 is formed at least in the regionsurrounding the electrodes 12. It should be noted that the electrodes 12refer to the portions connected to the leads 3, and this definition isalso used in all of the subsequent embodiments. Besides, whenconsidering the provision of the region for forming the externalelectrodes 5, although not shown in FIG. 5, it is possible similarly toprovide the external electrodes 5 so that the stress relieving layer 7is on the outside of the electrodes 12, and leads 3 are provided to bebrought out thereon. The fabrication process described below and shownin FIGS. 1A to 4C describes an example based on the assumption thatthere is also a stress relieving layer 7 provided on the outside of theelectrodes 12 shown in FIG. 5.

The electrodes 12 are shown as an example of the so-called peripheralelectrode type positioned on the periphery of the semiconductor chip 1,but equally an area array layout of semiconductor chip, in which theelectrodes are formed in a region inside the peripheral region of thesemiconductor chip, may be used. In this case, the stress relievinglayer may be formed so as to avoid at least some of the electrodes.

It should be noted that as shown in this drawing the external electrodes5 are provided not on the electrodes 12 of the semiconductor chip 1, butin the active region (the region in which the active elements areformed) of the semiconductor chip 1. By providing the stress relievinglayer 7 in the active region, and further positioning (bringing in) theleads 3 within the active region, the external electrodes 5 can beprovided within the active region. As a result, when laying out theexternal electrodes 5, the interior of the active region, that is tosay, a region of a particular area can be provided, and thus the degreeof freedom for positioning the external electrodes 5 is very greatlyincreased.

By bending the leads 3 on the stress relieving layer 7, the externalelectrodes 5 can be provided in a lattice. It should be noted that thisis not an essential feature of the invention, and the externalelectrodes 5 may be provided in such a way as not necessarily to form alattice. Besides, at the junction of the electrodes 12 and leads 3 thewidth of the electrodes 12 and the width of the leads 3 are such that:

leads 3<electrodes 12

but it is preferable that:

electrodes 12<leads 3

In particular, in the case that:

electrodes 12<leads 3

not only is the resistance of the leads 3 reduced, but also, since thestrength is increased, broken leads are prevented.

FIGS. 1A to 4C illustrate the first embodiment of the method of making asemiconductor device. These figures correspond to the section along theline I-I in FIG. 5, but show the state in which the stress relievinglayer is further present outside the area of FIG. 5. FIGS. 1A to 4C arepartial enlargements of a wafer, and in particular show one portioncorresponding to a semiconductor device.

First, by according to well-known techniques, normally in the statebefore dicing is carried out, electrodes 12 and other elements areformed on a wafer 10. It should be noted that in this example, theelectrodes 12 are formed of aluminum. As examples of other materials forthe electrodes 12 may equally be used aluminum alloy materials (forexample, aluminum-silicon or aluminum-silicon-copper, or the like) orcopper alloys.

Besides, on the surface of the wafer 10 is formed a passivation film(not shown in the drawings) being an oxidized film or the like, forpreventing chemical changes. The passivation film is formed not only toavoid the electrodes 12, but also to avoid the scribing line to whichdicing is carried out. By not forming the passivation film on thescribing line, during the dicing operation the generation of dust fromthe passivation film can be avoided, and the occurrence of cracks in thepassivation film can also be prevented.

As shown in FIG. 1A, on the wafer 10 having the electrodes 12 aphotosensitive polyimide resin is applied (using, for example, “the spincoating method”) to form a resin layer 14. The resin layer 14 has athickness preferably in the range 1 to 100 μm, and more preferably ofaround 10 μm. It should be noted that in the spin coating method, sincethere is a large quantity of polyimide resin wasted, a device may beused which employs a pump to eject a tape-shaped polyimide resin. As anexample of such a device may be given, for example, the FASultra-high-density ejection coating system (see U.S. Pat. No. 4,696,885)manufactured by the FAS company. It should be noted that the resin layer14 referred to here has the function of the stress relieving layer 7(see FIG. 5).

As shown in FIG. 1B, in the resin layer 14 are formed contact holes 14 aopposing the electrodes 12. Specifically, by means of exposure,development, and baking processes, the polyimide resin in the vicinityof the electrodes 12 is removed, whereby the contact holes 14 a areformed in the resin layer 14. It should be noted that in this figure,when the contact holes 14 a are formed, absolutely no region is left inwhich the resin layer 14 overlaps the electrodes 12. By leavingabsolutely none of the resin layer 14 on the electrodes 12, there is theadvantage that in the subsequent stages in which wiring and othermetallic components are provided, the electrical contact issatisfactory, but the construction is not necessarily restricted in thisway. That is to say, even in a construction in which on the outerperiphery of the electrodes 12 the resin layer 14 is applied, if holesare provided so that a part of the electrodes 12 is exposed, this willadequately achieve the objective. In this case, the number of bends inthe wiring layer is reduced, and as a result, a loss of wiringreliability due to broken leads and the like can be prevented. Here, thecontact holes 14 a have a taper. Here, a taper refers to the fact thatin the vicinity of the electrodes 12 (contact portion), the thickness ofthe resin layer 14 reduces closer to the electrodes 12. As a result, atthe edges where the contact holes 14 a are formed, the resin layer 14 isformed with an inclination. A formation of this type can be achieved byselection of the conditions of exposure and development. Furthermore, bytreatment of the electrodes 12 by a plasma of O₂, CF₄, or the like, evenif a small amount of the polyimide resin is left remaining on theelectrodes 12, the polyimide resin can be completely removed. The resinlayer 14 formed in this way forms the stress relieving layer in thecompleted semiconductor device.

It should be noted that in this example a photosensitive polyimide resinis used as the resin, but a nonphotosensitive resin may equally be used.For example, a silicone denatured polyimide resin, an epoxy resin, or asilicone denatured epoxy resin, or the like, being a material with astress relieving function having a low Young's modulus (not exceeding1×10¹⁰ Pa) when solidified, may be used. If a nonphotosensitive resin isused, thereafter using a photoresist, the required form is obtainedafter passing through a photographic process.

As shown in FIG. 1C, a chromium (Cr) layer 16 is formed by sputteringover the whole surface of the wafer 10. The wiring is finally formedfrom this chromium (Cr) layer 16. The chromium (Cr) layer 16 is formedover both the electrodes 12 and the resin layer 14. Here, the materialof the chromium (Cr) layer 16 is selected to have good adhesion with thepolyimide forming the resin layer 14. Alternatively, when resistance tocracks is considered, aluminum, an alloy of aluminum such asaluminum-silicon or aluminum-copper, an alloy of copper, copper (Cu), ora ductile metal such as gold may be used. If titanium, which hasexcellent moisture resistance, is selected, lead breakages due tocorrosion can be prevented. Titanium also has preferred adhesion withrespect to polyimide, and titanium-tungsten may also be used.

When the adhesion with the chromium (Cr) layer 16 is considered, it ispreferable for the surface of the resin layer 14 of polyimide or thelike to be roughened. For example, by carrying out dry processing byexposing to a plasma (O₂, CF₄), or wet processing with an acid oralkali, the surface of the resin layer 14 can be roughened.

Besides, since within the contact holes 14 a the edges of the resinlayer 14 are inclined, in this region the chromium (Cr) layer 16 isformed to be similarly inclined. In the semiconductor device which isthe finished product the chromium (Cr) layer 16 forms the leads 3 (seeFIG. 5), and also during the fabrication process serves as a layer toprevent dispersion of the polyimide resin at the time of thereafterforming the layer. It should be noted that the dispersion preventinglayer is not restricted to chromium (Cr), and all of the above-mentionedwiring materials are also effective.

As shown in FIG. 1D, on the chromium (Cr) layer 16, a photoresist isapplied to form a resist layer 18.

As shown in FIG. 1E, by means of exposure, development, and bakingprocesses, a part of the resist layer 18 is removed. The remainingresist layer 18, is formed from the electrodes 12 in the direction ofthe center of the resin layer 14. In more detail, the remaining resistlayer 18 is formed so that on the resin layer 14 the portion of theresist layer 18 on one electrode 12 and the portion of the resist layer18 on another electrode 12 are not continuous (are mutuallyindependent).

Next, leaving only the region covered by the resist layer 18 shown inFIG. 1E (that is to say, with the resist layer 18 as a mask), thechromium (Cr) layer 16 is etched, and the resist layer 18 is removed.With this, in these previous processes metal thin film formationtechnology in wafer processing is applied. The chromium (Cr) layer 16thus etched is shown in FIG. 2A.

In FIG. 2A, the chromium (Cr) layer 16 is formed extending from theelectrodes 12 over the resin layer 14. In more detail, the chromium (Cr)layer 16 is formed so as not to connect one electrode 12 to anotherelectrode 12. That is to say, the chromium (Cr) layer 16 is formed insuch a way that the wiring corresponding to the electrodes 12 can beformed. It should be noted that if the same signals are input or output,it is not necessary for electrodes 12 to be necessarily independent, anda piece of wiring carrying the same signal may equally be integrallyformed.

As shown in FIG. 2B, above the topmost layer including at least thechromium (Cr) layer 16, a copper (Cu) layer 20 is formed by sputtering.The copper (Cu) layer 20 forms an under-layer for forming externalelectrodes. Alternatively, in place of the copper (Cu) layer 20, anickel (Ni) layer may be formed.

As shown in FIG. 2C, on the copper (Cu) layer 20 is formed a resistlayer 22 (photoresist), and as shown in FIG. 2D, a part of the resistlayer 22 is subjected to exposure, development, and baking processes,and removed. In this way, as for the region removed, at least a part ofthe resist layer 22 positioned over the resin layer 14, and over thechromium (Cr) layer 16 is removed.

As shown in FIG. 2E, in the region in which the resist layer 22 ispartially removed, a seat 24 is formed. The seat 24 is formed by copper(Cu) plating, and is such that a solder balls can be formed thereon. Asa result, the seat 24 is formed on the copper (Cu) layer 20, and iselectrically connected through this copper (Cu) layer 20 and thechromium (Cr) layer 16 to the electrodes 12.

As shown in FIG. 3A, on the seat 24, solder 26 which will form solderballs as the external electrodes 5 (see FIG. 5) is formed as a thickfilm. This thickness is determined by the amount of solder correspondingto the ball diameter required when at a later state the solder balls areformed. The layer of solder 26 is formed by electroplating, printing, orthe like.

As shown in FIG. 3B, the resist layer 22 shown in FIG. 3A is removed,and the copper (Cu) layer 20 is etched. In this way, the seat 24 forms amask, the copper (Cu) layer 20 remains only under this seat 24 (see FIG.3C). Next, the solder 26 on the seat 24 is formed into balls of at leasthemispherical shape by wet-back, making solder balls (see FIG. 3D).Here, wet-back refers to a process in which after forming a soldermaterial on the position of forming external electrodes, reflow iscarried out to form approximately spherical bumps.

By means of the above process, solder balls are formed as the externalelectrodes 5 (see FIG. 5). Next, processes for meeting the objectives ofpreventing the oxidation of the chromium (Cr) layer 16 or the like, ofimproving moisture resistance in the finished semiconductor device, ofproviding mechanical protection for the surface, and so forth, arecarried out as shown in FIGS. 4A and 4B.

As shown in FIG. 4A, a photosensitive solder resist layer 28 is formedby application over the whole surface of the wafer 10. Then, by carryingout exposure, development, and baking processes, the portion of thesolder resist layer 28 covering the solder 26 and the neighboring regionis removed. In this way, the remaining solder resist layer 28 acts toprevent oxidation, and as a protective film in the finishedsemiconductor device, and further forms a protective layer for thepurpose of improving moisture resistance. Next a test for electricalcharacteristics is carried out, and if required, a product number andmanufacturer's name are printed.

Next, dicing is carried out, and as shown in FIG. 4C, individualsemiconductor devices are separated. Here, the dicing position (scribingline), as will be clear from a comparison of FIGS. 4B and 4C, is such asto avoid the resin layer 14. As a result, since dicing is only carriedout on the wafer 10 having no passivation film or the like, problemsinvolved in cutting through a number of layers of different materialscan be avoided. The dicing process is carried out by a conventionalmethod. It should be noted that FIGS. 4A and 4B show as far as anintermediate point of the resin layer 14 positioned on the outside ofthe electrodes, but FIG. 4C shows as far as a scribing line exceedingthe resin layer 14 positioned on the outside of the electrodes.

With a semiconductor device formed in this way, the resin layer 14 formsa stress relieving layer 7 (see FIG. 5), and therefore stress occurringbecause of differences in coefficients of thermal expansion between acircuit board (not shown in the drawings) and the semiconductor chip 1(see FIG. 5) is alleviated.

According to the above described method of making a semiconductordevice, almost all steps are completed within the stage of waferprocessing. In other words, the step in which the external terminals forconnection to the board on which mounting is to take place is carriedout within the stage of wafer processing, and it is not necessary tocarry out the conventional packaging process, that is to say, in whichindividual semiconductor chips are handled, and for each individualsemiconductor chip an inner lead bonding process and external terminalformation process are carried out. Besides, when the stress relievinglayer is formed, a substrate such as a patterned film is not required.For these reasons, a semiconductor device of low cost and high qualitycan be obtained.

Besides, in this example, there may be two or more wiring layers.Generally, when layers are superimposed the layer thickness increases,and the wiring resistance can be reduced. In particular, when one layerof the wiring is of chromium (Cr), since copper (Cu) or gold has a lowerelectrical resistance than chromium (Cr), a combination makes itpossible to reduce the wiring resistance. Alternatively, a titaniumlayer may be formed on the stress relieving layer, and on this titaniumlayer a nickel layer or a layer of platinum and gold may be formed.Besides, two layers of platinum and gold, may also be used for thewiring.

Second Embodiment

FIGS. 6A to 7C illustrate the second embodiment of the method of makinga semiconductor device. This embodiment differs from the firstembodiment in the steps in FIG. 3A and subsequent steps, and in thesteps up to FIG. 2E is the same as the first embodiment. Therefore,since the wafer 110, electrodes 112, resin layer 114, chromium (Cr)layer 116, copper (Cu) layer 120, resist layer 122, and seat 124 shownin FIG. 6A are the same as the wafer 10, electrodes 12, resin layer 14,chromium (Cr) layer 16, copper (Cu) layer 20, resist layer 22, and seat124 shown in FIG. 2E, and the method of fabrication is the same as shownin FIGS. 1A to 2E, description is omitted here.

In this embodiment, as shown in FIG. 6A, a thin solder film 126 isformed by plating on the seat 124, and the resist layer 122 is removed,as shown in FIG. 6B. Furthermore, with the thin solder film 126 as aresist, as shown in FIG. 6C the copper (Cu) layer 120 is etched.

Next, as shown in FIG. 7A a photosensitive solder resist layer 128 isformed over the whole surface of the wafer 110, and as shown in FIG. 7B,the solder resist layer 128 in the region of the seat 124 is removed byexposure, development, and baking processes.

Next, as shown in FIG. 7C, on the seat 124 where the thin solder film126 remains, a thick solder film 129, thicker than the thin solder film126 is formed by plating. This is carried out by electroless plating.The thick solder film 129 is then subjected to wet-back, whereby in thesame manner as shown in FIG. 3, balls of at least hemispherical shapeare formed. In this way, the thick solder film 129 forms the solderballs of the external electrodes 5 (see FIG. 5). The subsequent processis the same as in the first embodiment described above. It should benoted that the thin solder film 126 and thick solder film 129 may beplated in that order, and thereafter a photosensitive solder resistlayer (step of FIG. 7A) may be formed.

According to this embodiment again, almost all steps can be carried outwithin the stage of wafer processing. It should be noted that in thisembodiment, the thick solder film 129 is formed by electroless plating.As a result, the seat 124 may be omitted, and the thick solder film 129formed directly on the copper (Cu) layer 120.

Third Embodiment

FIGS. 8A to 9D illustrate the third embodiment of the method of making asemiconductor device.

Since the wafer 30, electrodes 32, resin layer 34, chromium (Cr) layer36, copper (Cu) layer 40 and resist layer 42 shown in FIG. 8A are thesame as the wafer 10, electrodes 12, resin layer 14, chromium (Cr) layer16, copper (Cu) layer 20, and resist layer 22 shown in FIG. 2C, and themethod of fabrication is the same as shown in FIGS. 1A to 2C,description is omitted here.

Next, a part of the resist layer 42 shown in FIG. 8A is removed byexposure, development, and baking processes. In more detail, as shown inFIG. 8B, only the resist layer 42 positioned over the chromium (Cr)layer 36 forming the wiring is left, and in other areas the resist layer42 is removed.

Next, the copper (Cu) layer 40 is etched and the resist layer 42 isremoved, so that as shown in FIG. 8C, the copper (Cu) layer 40 is leftonly on the chromium (Cr) layer 36. In this way, the wiring is formed asa two-layer construction from the chromium (Cr) layer 36 and copper (Cu)layer 40.

Next, as shown in FIG. 8D, a photosensitive solder resist is applied,and a solder resist layer 44 is formed.

As shown in FIG. 9A, in the solder resist layer 44 are formed contactholes 44 a. The contact holes 44 a are formed over the resin layer 34and over the copper (Cu) layer 40 which is the surface layer of thetwo-layer wiring. It should be noted that the formation of the contactholes 44 a is carried out by exposure, development, and bakingprocesses. Alternatively, the solder resist may be printed leaving holesin predetermined positions so as to form the contact holes 44 a.

Next, a solder cream 46 is printed in the contact holes 44 a to form araised shape (see FIG. 9B). The solder cream 46 is formed by a wet-backprocess into solder balls as shown in FIG. 9C. Next, dicing is carriedout, and the individual semiconductor device shown in FIG. 9D areobtained.

In this embodiment, the seat for the solder balls is omitted, and theprinting of a solder cream is used, simplifying the formation of thesolder balls, and also reducing the number of steps in the fabricationprocess.

Besides, the wiring of the fabricated semiconductor device is two-layer,of chromium (Cr) and copper (Cu). Here, chromium (Cr) has good adhesionwith respect to the resin layer 34 formed of polyimide resin, and thecopper (Cu) has good resistance to the formation of cracks. The goodresistance to cracks allows lead breaks and damage to the electrodes 32or active elements to be prevented. Alternatively, a copper (Cu) andgold two-layer, chromium (Cr) and gold two-layer, or chromium (Cr),copper (Cu), and gold three-layer wiring construction is also possible.

This embodiment is an example of not using a seat, but it goes withoutsaying that it is also possible to provide a seat.

Fourth Embodiment

FIG. 10 illustrates the fourth embodiment of the method of making asemiconductor device.

Since the wafer 130, electrodes 132, resin layer 134, chromium (Cr)layer 136, copper (Cu) layer 140 and solder resist layer 144 shown inthis figure are the same as the wafer 30, electrodes 32, resin layer 34,chromium (Cr) layer 36, copper (Cu) layer 40 and solder resist layer 44shown in FIG. 9A, and the method of fabrication is the same as shown inFIGS. 8A to 9A, description is omitted here.

In this embodiment, in place of the solder cream 46 used in FIG. 9B, tothe contact holes 144 a formed in the solder resist layer 144 flux 146is applied and solder balls 148 are disposed thereon. Thereafter, awet-back process, inspection, stamping, and dicing processes are carriedout.

According to this embodiment, the preformed solder balls 148 are put inplace, forming the external electrodes 5 (see FIG. 5). Besides, comparedwith the first and second embodiments, the seat 24 or 124 can beomitted. Furthermore, the leads 3 (see FIG. 5) are of a two-layerconstruction of the chromium (Cr) layer 136 and copper (Cu) layer 140.

This embodiment is an example of not using a seat, but it goes withoutsaying that it is also possible to provide a seat.

Fifth Embodiment

FIGS. 11A to 12C illustrate the fifth embodiment of the method of makinga semiconductor device.

First, as shown in FIG. 11A, a glass plate 54 is adhered to a wafer 50having electrodes 52. In the glass plate 54 are formed holes 54 acorresponding to the electrodes 52 of the wafer 50, and an adhesive 56is applied.

The coefficient of thermal expansion of the glass plate 54 has a valuebetween the coefficient of thermal expansion of the wafer 54 forming thesemiconductor chip and the coefficient of thermal expansion of thecircuit board on which the semiconductor device is mounted. Because ofthis, since the coefficient of thermal expansion varies in order of thesemiconductor chip obtained by dicing of the wafer 54, the glass plate54, and the circuit board (not shown in the drawings) on which thesemiconductor device is mounted, the differences in the coefficient ofthermal expansion at the junctions is reduced, and the thermal stress isreduced. That is to say, the glass plate 54 acts as the stress relievinglayer. It should be noted that in place of the glass plate 54 a ceramicplate may also be used, provided that it has a similar coefficient ofthermal expansion. Then, when the glass plate 54 is adhered to the wafer50, adhesive 56 which has entered the holes 54 is removed by an O₂plasma process, as shown in FIG. 11B.

Next, as shown in FIG. 11C, on the glass plate 54, being the wholesurface of the wafer 50, an aluminum layer 58 is formed by sputtering.Thereafter, if a film is formed on the surface of the holes 54, thealuminum, which is susceptible to lead breaks, can be protected. Next,as shown in FIG. 12A a resist layer 59 is formed, and as shown in FIG.12B, exposure, development, and baking processes are used to remove apart of the resist layer 59. The part of the resist layer 59 removed ispreferably the area other than the portion where the wiring pattern isformed.

In FIG. 12B, the resist layer 59 is left extending from over theelectrodes 52 to over the glass plate 54. Besides, it is separated so asnot to connect from over one electrode 52 to over another electrode 52.

Next, when the aluminum layer 58 is etched, as shown in FIG. 12C, thealuminum layer 58 is left in the region to form the wiring. That is tosay, the aluminum layer 58 extends from the electrodes 52 over the glassplate 54 to form the wiring. Besides, the aluminum layer 58 is formed sothat different electrodes 52 are not electrically connected, and thewiring is provided for individual electrodes 52. Alternatively, if it isnecessary for a plurality of electrodes 52 to be electrically connectedtogether, the aluminum layer 58 may be formed so as to provide thecorresponding wiring. It should be noted that for the wiring, in placeof the aluminum layer 58 may also be applied any of the materialsselected in the first embodiment.

By means of the above process, since the wiring from the electrodes 52is formed, solder balls are formed on the aluminum layer 58 being thewiring, and individual semiconductor devices are cut from the wafer 50.These steps can be carried out in the same way as in the firstembodiment.

According to this embodiment, the glass plate 54 has holes 54 a, but theformation of the holes 54 a is easy. Therefore, with respect to theglass plate 54 patterning beforehand to form bumps or wiring is notnecessary. Besides, for the steps such as that of forming the aluminumlayer 58 being the wiring, metal thin film formation technology in waferprocessing is applied, and almost all steps are completed within thestage of wafer processing.

It should be noted that on the glass plate 54 may be provided a separatestress absorbing layer, of for example polyimide resin or the like as inthe first embodiment. In this case, since the stress absorbing layer isonce again provided, the coefficient of thermal expansion of the glassplate 54 may be the same as that of silicon.

Sixth Embodiment

FIGS. 13A to 13D illustrate the sixth embodiment of the method of makinga semiconductor device. In this example, as the stress relieving layeris selected a polyimide plate preformed in plate shape. In particular,polyimide includes compositions with a low Young's modulus, andtherefore such a composition is selected as the stress relieving layer.It should be noted that alternatively, for example, a plastic plate orglass epoxy or similar composite plate may be used. In this case, it ispreferable to use the same material as the board on which mounting takesplace whereby the difference in the coefficient of thermal expansion isremoved. In particular, since at present the use of a plastic substrateas the mounting board is common, it is effective to use a plastic plateas the stress relieving layer.

First, as shown in FIG. 13A, a polyimide plate 64 is adhered to a wafer60 having electrodes 62, as shown in FIG. 13B. It should be noted thatan adhesive 66 has been previously applied to the polyimide plate 64. Itshould also be noted that further improvement will be obtained byselecting as the adhesive 66 a material having a stress relievingfunction. Specific examples of adhesives having a stress relievingfunction are for example thermoplastic polyimide resin, silicone resin,or the like.

Next, as shown in FIG. 13C, in the region corresponding to theelectrodes 62, contact holes 64 a are formed, using for example anexcimer laser, and as shown in FIG. 13D, an aluminum layer 68 is formedby sputtering. It should be noted that in place of the aluminum layer 68may also be applied any of the materials selected in the firstembodiment.

In this way, the same state as shown in FIG. 11C is reached, andtherefore thereafter by carrying out the steps in FIG. 12A andsubsequent figures, the semiconductor device can be fabricated.

According to this embodiment, since a polyimide plate 64 without evenany holes being formed is used, a patterned substrate is not required.Other benefits are the same as for the first to fifth embodimentsdescribed above.

As another embodiment, the stress relieving layer may have holes formedmechanically in advance by drilling or similar means, and a positioningprocess may be used for subsequent alignment on the wafer. It is alsopossible to provide the holes by non-mechanical means, such as chemicaletching or dry etching. It should be noted that if holes are formed bychemical etching or dry etching, this may be carried out on the wafer ina previous preparatory step.

Seventh Embodiment

FIGS. 14A to 17C illustrate the seventh embodiment of the method ofmaking a semiconductor device, and correspond to a section along theline I-I in FIG. 18. It should be noted that FIG. 18 illustrates asemiconductor device relating to the seventh embodiment.

In this embodiment, the step of exposing bumps 205 from a solder resistlayer 228 (see FIGS. 17A and 178) is shown in more detail than in thefirst embodiment. Otherwise, this is the same as the first embodiment.

First, by well-known techniques, on a wafer 210 electrodes 212 and otherelements are formed, and as shown in FIG. 14A, to the wafer 210 with theelectrodes 212 a photosensitive polyimide resin is applied, and a resinlayer 214 is formed. On the surface of the wafer 210, a passivation filmis formed, avoiding the electrodes 212 and scribing lines.

As shown in FIG. 14B, in the resin layer 214, contact holes 214 a areformed, corresponding to the electrodes 212.

As shown in FIG. 14C, a chromium (Cr) layer 216 is formed on the wholesurface of the wafer 210 by sputtering.

As shown in FIG. 14D, on the chromium (Cr) layer 216, a photoresist isapplied, forming a resist layer 218.

As shown in FIG. 14E, by means of exposure, development, and bakingprocesses, a part of the resist layer 218 is removed. The remainingresist layer 218 is formed to extend from the electrodes 212 in thedirection toward the center of the resin layer 214.

Next, as shown in FIG. 14E, the chromium (Cr) layer 216 is etched toleave only the region covered by the resist layer 218, and the resistlayer 218 is removed. The chromium (Cr) layer 216 etched in this way isshown in FIG. 15A.

In FIG. 15A, the chromium (Cr) layer 216 is formed to extend from theelectrodes 212 to the resin layer 214.

As shown in FIG. 15B, on the uppermost layer including at least thechromium (Cr) layer 216, a copper (Cu) layer 220 is formed bysputtering.

As shown in FIG. 15C, on the copper (Cu) layer 220 a resist layer 222 isformed, and as shown in FIG. 15D, a part of the resist layer 222 isremoved by exposure, development, and baking processes. In this way, asfor the region removed, at least a part of the resist layer 222 which isboth over the resin layer 214, and over the chromium (Cr) layer 216 isremoved.

As shown in FIG. 15E, in the region where the resist layer 222 ispartially removed, a seat 224 is formed. The seat 224 is formed bycopper (Cu) plating, and is such that solder balls are formed on itstop. As a result, the seat 224 is formed on the copper (Cu) layer 220,and connected through the copper (Cu) layer 20 and chromium (Cr) layer216 to the electrodes 212.

As shown in FIG. 16A, on the seat 224, for the purpose of forming solderballs as the bumps 205 (see FIG. 18), solder 226 is formed in a thicklayer. This thickness is determined by the amount of soldercorresponding to the ball diameter required for subsequent formation ofthe solder balls. The layer of solder 226 is formed by electroplating orprinting.

As shown in FIG. 16B, the resist layer 222 shown in FIG. 16A is removed,and the copper (Cu) layer 220 is etched. In this way, the seat 224 actsas a mask, and only the copper (Cu) layer 220 under the seat 224 remains(see FIG. 16C). Next, the solder 226 on the seat 224 is subjected to awet-back process, whereby balls of at least hemispherical shape areformed, thus becoming the solder balls (see FIG. 16D).

By means of the above process, solder balls are formed as the bumps 205(see FIG. 18). Next, processes for meeting the objectives of preventingthe oxidation of the chromium (Cr) layer 216 or the like, of improvingmoisture resistance in the finished semiconductor device, of providingmechanical protection for the surface, and so forth, are carried out asshown in FIGS. 17A and 17B.

As shown in FIG. 17A, a resin is applied (by spin coating, dripping, orthe like) over the whole surface of the wafer 210, and the solder resistlayer 228 is formed.

In this embodiment, the solder resist layer 228 is also formed over thebumps 205. That is to say, the solder resist layer 228 may be formedover the whole surface of the wafer 210, and forming to avoid the bumps205 is not necessary, as a result of which a simple application processis sufficient.

Here, the resin is applied overall, including the bumps 205, and thenfor example is formed into a film by hardening or another process,whereupon as shown in FIG. 17A, photosensitive resin applied to thebumps 205 flows over the surface of the wafer 210, as a result of whichthe thickness of the solder resist layer 228 varies. That is to say, thesolder resist layer 228 formed on the surface of the bumps 205 is thin,and other parts of the solder resist layer 228 formed on the wafersurface 10 is thick.

At this point, dry etching is carried out on such a solder resist layer228. In particular, as the dry etching process is carried outconventional isotropic etching. Then, as shown in FIG. 17B, when thethin solder resist layer 228 on the bumps 205 is etched and removed, theetching process is completed. At this time, the thick solder resistlayer 228 on the wafer 210 remains. By this means, the solder resistlayer 228 can be left on the surface of the wafer 210 while avoiding thebumps 205, and this solder resist layer 228 forms a protective layer. Inother words, the remaining solder resist layer 228 acts to preventoxidation, and as a protective film in the finished semiconductordevice, and further forms a protective layer for the purpose ofimproving moisture resistance. Next a test for electricalcharacteristics is carried out, and if required, a product number andmanufacturer's name are printed.

By means of the above process, a lithography process on the solderresist layer 228 is not required, and the processing can be simplifiedleading to a reduction in cost.

Next, dicing is carried out, and as shown in FIG. 17C, and the wafer 210is cut into semiconductor chips 201. Here, the dicing position, as willbe clear from a comparison of FIGS. 17B and 17C, is such as to avoid theresin layer 214. As a result, since dicing is only carried out on thewafer 210, problems involved in cutting through a number of layers ofdifferent materials can be avoided. The dicing process is carried out bya conventional method.

With respect to a semiconductor device 200 fabricated as describedabove, since the resin layer 214 forms the stress relieving layer 207(see FIG. 18), the stress created by the difference in coefficient ofthermal expansion between the circuit board (not shown in the drawings),and the semiconductor chip 201 (see FIG. 18) can be absorbed.

FIG. 18 is a plan view of the semiconductor device relating to thisembodiment. The semiconductor device 200 is classified as a so-calledCSP, and as a result, the leads 3 are formed from the electrodes 212 ofthe semiconductor chip 201 in the direction toward the center of theactive surface 201 a, and on the wiring 203 are formed bumps 205. All ofthe bumps 205 are provided on the stress relieving layer 207, andtherefore when mounted on a circuit board (not shown in the drawings)the stress can be absorbed. Besides, on the wiring 203, the solderresist layer 228 is formed as a protective layer.

It should be noted that in the above described embodiment, thesemiconductor device is fabricated with almost the whole of the processin the wafer processing, and as a result the formation of the solderresist layer 228 as a protective layer was carried out during the waferprocessing, but this is not a limitation. For example, an overall layerof resin may be applied to individual semiconductor devices includingbumps, and then isotropic dry etching may be carried out to remove theresin from the bumps.

Eighth Embodiment

FIGS. 19A and 19B illustrate the eighth embodiment of the method ofmounting of a semiconductor device. Here, a semiconductor device 300 hasa similar construction to the semiconductor device 200 shown in FIG.17C, except that a flux layer 232 is formed from over bumps 230. That isto say, wiring 238 is brought out from electrodes 236 of a semiconductorchip 234, and subjected to pitch conversion, then bumps 230 are formedon the wiring 238. Besides, since the wiring 238 is formed on the stressrelieving layer 240, stress applied to the bumps 230 can be absorbed.

Here, the flux layer 232 is formed by applying an overall layer of flux,turning upward the bumps 230 of the semiconductor device 300. Thisapplication is carried out by spin coating or dripping. Besides, it ispreferable that the flux used is such that when heated, the residuechanges by chemical reaction into a thermoplastic polymer (for example,NS-501 manufactured by Nihon Speria). By this means, since the residueis chemically stable, ionization does not occur, and the electricalinsulation properties are excellent.

The semiconductor device 300 having such a flux layer 232 is, as shownin FIG. 19A, mounted on a circuit board 250.

More specifically, as shown in FIG. 19B, with the flux layer 232interposed, the bumps 230 are positioned on wiring 252 and 254 on thecircuit board 250, and the semiconductor device 300 is mounted.

Next, by means of a reflow process, the solder forming the bumps 230 ismelted, and the bumps 230 and wiring 252 and 254 are connected. The fluxlayer 232 is consumed during this soldering step. However, the fluxlayer 232 is consumed only in the vicinity of the bumps 230, and inother regions the flux layer 232 remains. The remaining flux layer 232is heated in the reflow process, and as a result turns into athermoplastic polymer resin, forming an insulating layer. As a result,the residue of this flux layer 232 forms a protective layer over thesurface of the semiconductor device 300 on which the bumps 230 areformed.

Thus, according to this embodiment, the step of applying the flux iscombined with the step of forming the protective layer, and therefore astep of forming a protective layer by lithography or the like is notrequired.

The invention is not restricted to the above described embodiments, andvarious modifications are possible. For example, the abovedescribed-embodiments apply the invention to a semiconductor device, butthe invention can be applied to various surface-mounted electroniccomponents, whether active or passive. As electronic components, forexample, may be cited resistors, capacitors, coils, oscillators,filters, temperature sensors, thermistors, varistors, variableresistors, and fuses.

Other Embodiments

The invention is not restricted to the above described embodiments, andvarious modifications are possible. For example, the above describedembodiments apply the invention to a semiconductor device, but theinvention can be applied to various surface-mounted electroniccomponents, whether active or passive.

FIG. 20 shows an example of a surface-mounted electronic component towhich the invention is applied. In this figure, an electronic component400 has a chip portion 402 at both ends of which are provided electrodes404, and for example, this may be a resistor, capacitor, coil,oscillator, filter, temperature sensor, thermistor, varistor, variableresistor, or fuse. The electrodes 404 have, in the same way as in theembodiments described above, wiring 408 formed with a stress relievinglayer 406 interposed. On this wiring 408, bumps 410 are formed.

Besides, FIG. 21 also shows an example of a surface-mounted electroniccomponent to which the invention is applied; this electronic component420 has electrodes 424 formed on the mounting surface of a chip portion422, and wiring 428 formed with a stress relieving layer 426 interposed.On this wiring 428, bumps 430 are formed.

It should be noted that the method of fabrication of these electroniccomponents 400 and 420 is the same as in the above describedembodiments, and therefore description is omitted here. Besides, benefitobtained by formation of the stress relieving layers 406 and 426 is thesame as in the above described embodiments.

Next, FIG. 22 shows an example in which a protective layer is formed ona semiconductor device to which the invention is applied. Asemiconductor device 440 shown in this figure is the semiconductordevice shown in FIG. 4C on which a protective layer 442 is formed, andsince except for the protective layer 442 this is the same as thesemiconductor device shown in FIG. 4C, description is omitted here.

The protective layer 442 on the semiconductor device 440 is formed onthe side opposite to the mounting surface, that is to say, on the rearsurface. By so doing, the rear surface can be protected from damage.

Furthermore, damage to the semiconductor chip itself caused by cracksinitiated by damage to the rear surface can be prevented.

The protective layer 442 is preferably formed on the rear surface of thewafer before cut into individual semiconductor devices 440. If this isdone, a plurality of semiconductor devices 440 can have the protectivelayer 442 formed simultaneously. In more detail, it is preferable thatafter the metal thin film forming process is completed, the protectivelayer 442 is formed on the wafer. By so doing, the metal thin filmforming process can be carried out smoothly.

The protective layer 442 is preferably of a material which can withstandthe high temperature of the semiconductor device 440 reflow process. Inmore detail, it is preferable that it can withstand the temperaturewhich is the melting point of the solder. That is to say, it ispreferable that the protective layer 442 is of a material which has amelting point not less than the melting point of the solder. Besides, asthe protective layer 442 may be used, for example, a resin. In thiscase, the protective layer 442 may be formed by application of a resinused as a potting resin. Alternatively, the protective layer 442 may beformed by attaching a sheet of material having either tackiness oradhesion. This sheet of material may be either organic or inorganic.

In this way, since the surface of the semiconductor device is coveredwith a substance other than silicon, for example, the marking qualitiesare improved.

Next, FIG. 23 shows an example in which a radiator is fitted to asemiconductor device to which the invention is applied. A semiconductordevice 450 shown in this figure is the semiconductor device shown inFIG. 4C to which a radiator 452 is fitted, and since except for theradiator 452 this is the same as the semiconductor device shown in FIG.4C, description is omitted here.

The radiator 452 on the semiconductor device 450 is formed on the sideopposite to the mounting surface, that is to say, on the rear surface,with a thermally conducting adhesive 454 interposed. By so doing, theheat dissipation properties are improved. The radiator 452 has aplurality of fins 456, and these are commonly formed of copper, copperalloy, aluminum nitride, or the like. It should be noted that in thisexample, an example with fins is shown, but a radiator without fins(radiating plate) may also be used to obtain an appropriate radiationeffect. In this case, since a simple plate is attached, the handling issimple, and the cost can also be reduced.

In the above described embodiments, solder bumps or gold bumps areprovided in advance as external terminals on the semiconductor device,but as other examples, without using solder bumps or gold bumps on thesemiconductor device, for example, a seat of copper or the like may beused, as its is, for an external terminal. It should be noted that inthis case, it is necessary to provide solder on the connecting portion(land) of the mounting board for a semiconductor device (motherboard)before it is mounted.

Besides, the polyimide resin used in the above described embodiments ispreferably black. By using a black polyimide resin as the stressrelieving layer, operating faults when light impinges on thesemiconductor chip can be avoided, and also with an increase in thedurability with respect to light the reliability of the semiconductordevice can also be improved.

It should be noted that in FIG. 24 is shown, a circuit board 1000 onwhich is mounted an electronic component 1100 being a semiconductordevice or the like fabricated according to the methods of the abovedescribed embodiments. Moreover, as an electronic instrument providedwith this circuit board 1000, FIG. 25 shows a notebook personal computer1200.

1. A method of making a semiconductor device, the method comprising:providing a stress relieving layer on a first surface of a wafer onwhich a first electrode is formed such that the stress relieving layeravoids at least a part of the first electrode; forming a radiator on asecond surface of the wafer opposite to the first surface of the wafer;forming a wiring having a first portion, a second portion and a thirdportion, the first portion of the wiring being positioned on the firstelectrode, the second portion of the wiring being positioned on thestress relieving layer, the third portion of the wiring connecting thefirst portion of the wiring and the second portion of the wiring;forming a second electrode on at least a part of the second portion ofthe wiring; and cutting the wafer into individual pieces.
 2. The methodof making a semiconductor device of claim 1, the radiator having aplurality of fins.
 3. The method of making a semiconductor device ofclaim 1, the wiring being formed such that at least a part of the secondportion of the wiring having a width narrower than a width of the firstelectrode in a direction parallel to the first surface of the wafer inthe forming of the wiring.
 4. The method of making a semiconductordevice of claim 1, the cutting of the wafer performed after the formingof the second electrode.
 5. A method of making a semiconductor device,the method comprising: providing a resin layer on a first surface of awafer on which a first electrode is formed such that the resin layeravoids at least a part of the first electrode; forming a radiator on asecond surface of the wafer opposite to the first surface of the wafer;forming a wiring having a first portion, a second portion and a thirdportion, the first portion of the wiring being positioned on the firstelectrode, the second portion of the wiring being positioned on theresin layer, the third portion of the wiring connecting the firstportion of the wiring and the second portion of the wiring; forming asecond electrode on at least a part of the second portion of the wiring;and cutting the wafer into individual pieces.
 6. The method of making asemiconductor device of claim 5, the radiator having a plurality offins.
 7. The method of making a semiconductor device of claim 5, thewiring being formed such that at least a part of the second portion ofthe wiring having a width narrower than a width of the first electrodein a direction parallel to the first surface of the wafer in the formingof the wiring.
 8. The method of making a semiconductor device of claim5, the cutting of the wafer performed after the forming of the secondelectrode.